balanced and unbalanced regualtors

[gehadoski]

Hi all

A friend of mine told me that there is a differance between the balanced and unbalanced regulator (1st stage), if there is a failure in the regulator. The balanced will make a free flow but the unbalanced will block the flow of air.

Please tell me is this piece of information correct or not? If it is not correct what is the correct.

Note: I am talking about in case if there is a failure ONLY.

 

[rmediver2002]

No, this is not correct.

There really is not that much that can go wrong with a first stage other than deterioration or damage to the seals, in the event a seal does fail it is going to provide excess air "free flow" in both cases not secure the air.

A non-balanced unit provides a fluxuating intermediate pressure by allowing a metered amount of high pressure air into the system until it reaches equilibrium with the intermediate pressure setting, when the pressure difference is greatest the largest amount of air is flowing but as the pressure nears this equilibrium point the flow is very slight. These units are relying on spring tension to allow air into the system, it takes a signifigant drop in pressure to compress the spring far enough to reach that maximal flow rate. The other disadvantage to efficiency is that as tank pressure drops there is less force being exerted against the seat and spring so it requires a greater drop in pressure to open the seat.

A balanced unit works with the pressure of the air in the intermediate loop causing the seal to open, basically as that intermediate pressure decreases the seat drops open allowing a high flow of HP air into the loop, as the loop gains pressure it puts force on the seat and shuts it. Very efficient and the intermediate pressure remains at a constant instead of fluxuating based on the force (tank pressure) being applied to the seat.

 

[DA Aquamaster]

In hopefully easier to follow and more complete terms:

In an unbalanced piston first stage the incoming air from the tank pushes directly against the seat and the tank pressure helps open the valve.

This downstream force from the tank is assisted by the force of the mainspring in the first stage which tries to holds the piston (with the seat on the end of the piston shaft) open. A small hole in the side of the piston shaft allows air to flow through the shaft behind the seat to the head of the piston where the air enters a compression chamber and forces the piston and seat down on the orifice to close the valve. The intermediate pressure of the regulator is consequently determined by the pressure required to overcome the downstream force and the spring force holding the valve open.

So as the tank pressure drops, so the does the intermediate pressure. A drop of 12-15 psi is normal in most unbalanced piston first stages.

This has a slight and mostly unnoticeable effect on flow rate but will have a noticeable effect on a downstream second stage where the valve operates on the principle of downstream force and spring force being overcome by the force applied from the diaphragm through the lever to lift the seat from the orifice to open the valve. In this case as the IP falls, less downstream force is available to open the valve and more effort must come from the diaphragm pushing on the lever which means a slightly higher inhalation effort is required to provide the additional force to open the valve. So the reg gets harder to breathe at the end of the dive at low tank pressures (and isa nice clue that you are low on air).

With a balanced second stage, it is less of an issue as the valve is "balanced" with IP air on both sides of the valve and a drop in IP has less effect on the diaphragm/lever force required to open the valve.

Flow rates in an unbalanced first stage are limited not so much by the need for the air to squeeze through the gap between the seat and orifice (as this occurs in balanced second stages as well) but rather by the slower response time of the piston movement caused by the need for IP air to pass through the bleed hole and into the compression chamber.

A balanced piston first stage on the other hand uses a flow through piston design. The sharp edge of the orifice is on the end of the piston shaft and the seat is installed in the regulator body. The high pressure air however enters from the side and does not act directly on the piston mounted knife edged orifice or the seat. So downstream force from the tank is (mostly) not a factor and the intermediate pressure of the reg depends only on the mainspring force which is constant.

In a balanced piston reg, the air supplying the second stage comes from the compression chamber so a drop in pressure caused by inhalation immediately drops the IP slightly and causes the mainspring to open the valve. The air then flows around the end of the piston knife edge and through a large hole in the center of the piston shaft. You get some drop in IP during inhalation but it is normally less than the drop in an unbalanced second stage and the response time is much shorter.

There is still some force applied to the knife edge on the piston as its surface area is not zero but the downstream force related change in IP is only a few psi as the tank pressure falls from 3000 psi to 300 psi. The current trend is to make the end of the piston shaft with the orifice slightly larger than the middle of the shaft to account for the area of the knife edge and totally balance or even slightly overbalance the first stage.

An unbalanced diaphragm reg is different in that the tank pressure helps to hold the valve closed so the IP will increase instead of decrease as tank pressure drops. So an unbalaced second stage would breathe easier at the end of the dive than it does at the beginning.

Balancing a diaphragm first stage eliminates the tank pressure as a factor in opening the valve, and again IP is much more stable. Flow rates and response time however tend to be lower than a balanced piston first stage. Consequently, balanced diaphragm first stages will often use a larger internal chamber to store IP air or use some type of flow assist or high flow port arrangement to partially compensate for this slower response time and peak flow rate.

99.9% of all failures in a first stage will result in a freeflow situation where too much air is delivered. The only thing that will potentially stop the airflow would be breakage of the mainspring required to opent he valve in both piston and diaphragm designs. In some cases though the reg will still deliver air even with a broken mainspring. In any event breaking a mainspring is exceedingly rare in a properly designed reg to the point of being almost unheard of.

 

[quimby]

99.9% of all failures in a first stage will result in a freeflow situation where too much air is delivered. The only thing that will potentially stop the airflow would be breakage of the mainspring required to opent he valve in both piston and diaphragm designs. In some cases though the reg will still deliver air even with a broken mainspring. In any event breaking a mainspring is exceedingly rare in a properly designed reg to the point of being almost unheard of.

Dated info for sure but in 5 1/2 yrs in a dive shop the only failed stopped reg was one that someone experimented with O2 on a waterlung with a non O2 compatable lube. It kinda Mt St. Helened but that was the only one. Much more likly is badly restricted by the sintered filter having salt water on it and corroding to restriction which takes supprisingly little and is sometimes not that apparent. Changing those little guys is one good investment of $1

 

[DA Aquamaster]

A plugged filter is not a mechnical failure but rather a maintenence issue. It will afflict all first stage designs equally.

Partially open valves are another very common source of restricted airflow but it is also not a first stage mechanical design issue.

Second stages have far more potential to fail closed if subjected to large amounts of dirt, rocks or ice but that is not so bad as every diver should have an octo or alternate/redundant air source of some type.

 

[Hoosier]

Oh~~gee..

I hope I understood what you guys are talking about. So, in the plain english, which one is better?

 

[scubapro50]

Ok ... now that you have an answer from all the diving tech experts let me explain it to you in plain english ....... both a balance and unbalance will work fine for most diving. A unbalance regulator may breath a little harder at greater depth or when your air pressure is getting low. The unbalance regulators generaly have fewer parts which mean less trouble as a whole. A good unbalance regulator is the Scubapro MK2 which has been around 30 years ..... it's been called one of the best designs ever due to it's reliability and the fact it's been around for so long. I own a balance regulator (Scubapro MK10) for over 12 years and it's been great. A balance regulator (both 1st and 2nd stages balanced) will give you the best performance by supplying the greatest amount of air with less effort than an unbalance one.

 

[Hoosier]

[font=바탕]OK,[/font]

[font=바탕]Unbalanced reg:[/font]
[font=바탕]Pros: reliable due to the simple design[/font]
[font=바탕]Cons: a little bit hard to breathe[/font]

[font=바탕]Balanced reg:[/font]
[font=바탕]Pros: easy to breathe[/font]
[font=바탕]Cons: more complicated design -[/font]à[font=바탕] less reliable.[/font]

[font=바탕]Anything else?[/font]

[font=바탕]Thanks for your effort.[/font]

 

[DA Aquamaster]

Unbalanced Reg - $
Balanced Reg - $$

 

[SangP]

Hi,

What about the overbalanced 1st stage? How does that work and how much better are these regs compared to the unbal/bal regs?

Thanks

SangP